Doppler-nulling for directional networks (spatial awareness)

ABSTRACT

A system is disclosed. The system may include a receiver or transmitter node. The receiver or transmitter node may include a communications interface with a directional antenna element and a controller. The controller may include one or more processors and have information of own node velocity and own node orientation relative to a common reference frame. The receiver or transmitter node may be time synchronized to apply Doppler corrections associated with the receiver or transmitter node&#39;s own motions relative to the common reference frame. The common reference frame may be known to the receiver or transmitter node prior to the receiver node or transmitter receiving signals from a source.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to and claims priority from thefollowing U.S. Patent Applications:

(a) U.S. patent application Ser. No. 17/233,107, filed Apr. 16, 2021,which is incorporated by reference in its entirety;

(b) P.C.T. Patent Application No. PCT/US22/24653, filed Apr. 13, 2022,which claims priority to U.S. patent application Ser. No. 17/233,107,filed Apr. 16, 2021, all of which are incorporated by reference in itsentirety;

(c) U.S. patent application Ser. No. 17/408,156, filed Aug. 20, 2021,which claims priority to U.S. patent application Ser. No. 17/233,107,filed Apr. 16, 2021, all of which are incorporated by reference in itsentirety;

(d) U.S. patent application Ser. No. 17/541,703, filed Dec. 3, 2021,which is incorporated by reference in its entirety, which claimspriority to:

U.S. patent application Ser. No. 17/408,156, filed Aug. 20, 2021, whichis incorporated by reference in its entirety; and

U.S. patent application Ser. No. 17/233,107, filed Apr. 16, 2021, all ofwhich is incorporated by reference in its entirety;

(e) U.S. patent application Ser. No. 17/534,061, filed Nov. 23, 2021,which is incorporated by reference in its entirety;

(f) U.S. Patent Application No. 63/344,445, filed May 20, 2022, which isincorporated by reference in its entirety;

(g) U.S. patent application Ser. No. 17/857,920, filed Jul. 5, 2022,which is incorporated by reference in its entirety;

(h) U.S. Patent Application No. 63/400,138, filed Aug. 23, 2022, whichis incorporated by reference in its entirety;

(i) U.S. patent application Ser. No. 17/940,898, filed Sep. 8, 2022,which is incorporated by reference in its entirety;

(j) U.S. patent application Ser. No. 17/941,907, filed Sep. 9, 2022,which is incorporated by reference in its entirety;

(k) U.S. patent application Ser. No. 17/957,881, filed Sep. 30, 2022,which is incorporated by reference in its entirety; and

(l) U.S. patent application Ser. No. 17/990,491, filed Nov. 18, 2022,which is incorporated by reference in its entirety.

BACKGROUND

Mobile Ad-hoc NETworks (MANET; e.g., “mesh networks”) are known in theart as quickly deployable, self-configuring wireless networks with nopre-defined network topology. Each communications node within a MANET ispresumed to be able to move freely. Additionally, each communicationsnode within a MANET may be required to forward (relay) data packettraffic. Data packet routing and delivery within a MANET may depend on anumber of factors including, but not limited to, the number ofcommunications nodes within the network, communications node proximityand mobility, power requirements, network bandwidth, user trafficrequirements, timing requirements, and the like.

MANETs face many challenges due to the limited network awarenessinherent in such highly dynamic, low-infrastructure communicationsystems. Given the broad ranges in variable spaces, the challenges liein making good decisions based on such limited information. For example,in static networks with fixed topologies, protocols can propagateinformation throughout the network to determine the network structure,but in dynamic topologies this information quickly becomes stale andmust be periodically refreshed. It has been suggested that directionalsystems are the future of MANETs, but the potential of this future hasnot as yet been fully realized. In addition to topology factors,fast-moving platforms (e.g., communications nodes moving relative toeach other) experience a frequency Doppler shift (e.g., offset) due tothe relative radial velocity between each set of nodes. This Dopplerfrequency shift often limits receive sensitivity levels which can beachieved by a node within a mobile network.

Directional radio-frequency (RF) networks often spend considerableamounts of time scanning the physical space over which potential RFnetwork signals may exist. Because this scanning may be a lengthyprocess based on how precise the scan is, often it becomes necessary tosacrifice other potentially important system performance metrics (e.g.,size of scanned area, quantity/density and beam width of signals,sensitivity, range, and/or the like) to ensure timely discoveryperformance.

SUMMARY

A system is disclosed in accordance with one or more illustrativeembodiments of the present disclosure. In one illustrative embodiment,the system may include a receiver or transmitter node. In anotherillustrative embodiment, the receiver or transmitter node may include acommunications interface with a directional antenna element and acontroller. In another illustrative embodiment, the controller mayinclude one or more processors and have information of own node velocityand own node orientation relative to a common reference frame. Inanother illustrative embodiment, the receiver or transmitter node may betime synchronized to apply Doppler corrections associated with thereceiver or transmitter node's own motions relative to the commonreference frame. In another illustrative embodiment, the commonreference frame may be known to the receiver or transmitter node priorto the receiver node or transmitter receiving signals from a source.

This Summary is provided solely as an introduction to subject matterthat is fully described in the Detailed Description and Drawings. TheSummary should not be considered to describe essential features nor beused to determine the scope of the Claims. Moreover, it is to beunderstood that both the foregoing Summary and the following DetailedDescription are example and explanatory only and are not necessarilyrestrictive of the subject matter claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to the accompanyingfigures. The use of the same reference numbers in different instances inthe description and the figures may indicate similar or identical items.Various embodiments or examples (“examples”) of the present disclosureare disclosed in the following detailed description and the accompanyingdrawings. The drawings are not necessarily to scale. In general,operations of disclosed processes may be performed in an arbitraryorder, unless otherwise provided in the claims.

FIG. 1 is a diagrammatic illustration of two nodes in a simplifiedmobile ad hoc network (MANET) and individual nodes thereof according toexample embodiments of this disclosure.

FIG. 2A is a graphical representation of frequency shift profiles withinthe MANET of FIG. 1 .

FIG. 2B is a graphical representation of frequency shift profiles withinthe MANET of FIG. 1 .

FIG. 3 is a diagrammatic illustration of a transmitter node and areceiver node according to example embodiments of this disclosure.

FIG. 4A is a graphical representation of frequency shift profiles withinthe MANET of FIG. 3 .

FIG. 4B is a graphical representation of frequency shift profiles withinthe MANET of FIG. 3 .

FIG. 5 is a graph of sets for covering space.

FIG. 6 is a diagrammatic illustration of a transmitter node and areceiver node according to example embodiments of this disclosure.

FIG. 7 is a flow diagram illustrating a method according to exampleembodiments of this disclosure.

FIG. 8 is a time-based graphical representation of a plurality of pulsesof a scanning sequence, according to one or more embodiments of thepresent disclosure.

FIG. 9A is a diagrammatic illustration of multiple systems which aretime synchronized to utilize a common scanning sequence such that thereceiving angles and transmitting angles of each system will align,according to one or more embodiments of the present disclosure.

FIG. 9B is a diagrammatic illustration of FIG. 9A at a subsequent timestep where a particular transmitting angle and receiving angle ofdifferent systems are aligned, according to one or more embodiments ofthe present disclosure.

FIG. 10 is a graphical representation of an angular distribution ofantenna gain versus angle, according to one or more embodiments of thepresent disclosure.

FIG. 11 is a graphical representation of net frequency shift points anda frequency shift profile including a zero crossing based on the netfrequency shift points, according to one or more embodiments of thepresent disclosure.

DETAILED DESCRIPTION

Before explaining one or more embodiments of the disclosure in detail,it is to be understood that the embodiments are not limited in theirapplication to the details of construction and the arrangement of thecomponents or steps or methodologies set forth in the followingdescription or illustrated in the drawings. In the following detaileddescription of embodiments, numerous specific details may be set forthin order to provide a more thorough understanding of the disclosure.However, it will be apparent to one of ordinary skill in the art havingthe benefit of the instant disclosure that the embodiments disclosedherein may be practiced without some of these specific details. In otherinstances, well-known features may not be described in detail to avoidunnecessarily complicating the instant disclosure.

As used herein a letter following a reference numeral is intended toreference an embodiment of the feature or element that may be similar,but not necessarily identical, to a previously described element orfeature bearing the same reference numeral (e.g., 1, 1a, 1b). Suchshorthand notations are used for purposes of convenience only and shouldnot be construed to limit the disclosure in any way unless expresslystated to the contrary.

Further, unless expressly stated to the contrary, “or” refers to aninclusive or and not to an exclusive or. For example, a condition A or Bis satisfied by any one of the following: A is true (or present) and Bis false (or not present), A is false (or not present) and B is true (orpresent), and both A and B are true (or present).

In addition, use of “a” or “an” may be employed to describe elements andcomponents of embodiments disclosed herein. This is done merely forconvenience and “a” and “an” are intended to include “one” or “at leastone,” and the singular also includes the plural unless it is obviousthat it is meant otherwise.

Finally, as used herein any reference to “one embodiment”, “inembodiments” or “some embodiments” means that a particular element,feature, structure, or characteristic described in connection with theembodiment is included in at least one embodiment disclosed herein. Theappearances of the phrase “in some embodiments” in various places in thespecification are not necessarily all referring to the same embodiment,and embodiments may include one or more of the features expresslydescribed or inherently present herein, or any combination orsub-combination of two or more such features, along with any otherfeatures which may not necessarily be expressly described or inherentlypresent in the instant disclosure.

Broadly speaking, embodiments of the inventive concepts disclosed hereinare directed to methods and systems for achieving situational awarenessusing doppler nulling with directional antenna elements (e.g.,electronically scanned antennas (ESAs)). For example, at least one node(e.g., which may transmit signals and/or receive signals) may utilize adirectional (rather than omnidirectional) antenna element for improvedperformance. Embodiments may utilize time synchronized scanningsequences (along with directionality) to improve metrics such assignal-to-noise ratio, signal acquisition time, speed of attainingsituational awareness of attributes of surrounding nodes, range, and thelike. In some embodiments, synced scanning sequences are used so thatall transmitting angles of multiple systems are pointing in the samedirection at any point in time during a synced sequence, as well as allthe receiving angles, which are pointed in the opposite direction. Inthis regard, if a pulse happens to be sent towards a particular system,that particular system's receiving angle will be aimed in the oppositedirection the pulse was sent from, such that the receiving angle isconfigured to receive the pulse. Such a configuration may vastly improvethe ability to detect a relatively large quantity of nodes in arelatively short period of time over relatively large ranges, overrelatively large amounts of noise/interference, and the like. In someembodiments, a zero value or near zero value (e.g., or the like such asa zero crossing) of a calculated net frequency shift of a receivedsignal is used to determine a bearing angle between the source (e.g., Txnode) and the receiving node using a time-of-arrival of the receivedsignal. The bearing angle may be made more accurate by combining (e.g.,averaging) it with another bearing angle estimation determined from anangle of peak amplitude gain of the signal.

Some other communication protocols (e.g., typical communication methods)may require a higher signal to noise ratio (SNR) or scanning times thandirectional doppler nulling methods. For example, directional dopplernulling methods may allow for using relatively less power (e.g., watts)and a weaker signal, while still providing for situational awareness,than other methods.

It is noted that U.S. patent application Ser. No. 17/857,920, filed Jul.5, 2022, is at least partially reproduced by at least some (or all) ofthe illustrations of FIGS. 1-7 and at least some (or all) of thecorresponding language for FIGS. 1-7 below. For example, at least someexamples of doppler nulling methods and systems may be betterunderstood, in a nonlimiting manner, by reference to FIGS. 1-7 . Suchembodiments and examples are provided for illustrative purposes and arenot to be construed as necessarily limiting. For instance, inembodiments the transmitter node may be stationary rather than movingand/or vice versa.

Moreover, and stated for purposes of navigating the disclosure only (andwhich may save time when comparing differences between applications) andnot to be construed as limiting, descriptions that may more directlyrelate to language not necessarily simply reproduced from U.S. patentapplication Ser. No. 17/857,920 include the discussion and figures afterFIGS. 1-7 .

Referring now to FIGS. 1-7 , in some embodiments, a stationary receivermay determine a cooperative transmitter's direction and velocity vectorby using a Doppler null scanning approach in two dimensions. A benefitof the approach is the spatial awareness without exchanging explicitpositional information. Other benefits include discovery,synchronization, and Doppler corrections which are important forcommunications. Some embodiment may combine coordinated transmitterfrequency shifts along with the transmitter's motion induced Dopplerfrequency shift to produce unique net frequency shift signalcharacteristics resolvable using a stationary receiver to achievespatial awareness. Further, some embodiment may include athree-dimensional (3D) approach with the receiver and the transmitter inmotion.

Some embodiments may use analysis performed in a common reference frame(e.g., a common inertial reference frame, such as the Earth, which mayignore the curvature of Earth), and it is assumed that thecommunications system for each of the transmitter and receiver isinformed by the platform of its own velocity and orientation. Theapproach described herein can be used for discovery and tracking, butthe discussion here focuses on discovery which is often the mostchallenging aspect.

The meaning of the ‘Doppler Null’ can be explained in part through areview of the two-dimensional (2D) case without the receiver motion, andthen may be expounded on by a review of adding the receiver motion tothe 2D case, and then including receiver motion in the 3D case.

The Doppler frequency shift of a communications signal is proportionalto the radial velocity between transmitter and receiver, and anysignificant Doppler shift is typically a hindrance that should beconsidered by system designers. In contrast, some embodiments utilizethe Doppler effect to discriminate between directions with theresolution dictated by selected design parameters. Furthermore, suchembodiments use the profile of the net frequency shift as thepredetermined ‘Null’ direction scans through the angle space. Theresultant profile is sinusoidal with an amplitude that provides thetransmitter's speed, a zero net frequency shift when the ‘Null’direction aligns with the receiver, and a minimum indicating thedirection of the transmitter's velocity. It should be noted that thatthe transmitter cannot correct for Doppler in all directions at one timeso signal characteristics are different in each direction and aredifferent for different transmitter velocities as well. It is exactlythese characteristics that the receiver uses to determine spatialawareness. The received signal has temporal spatial characteristics thatcan be mapped to the transmitter's direction and velocity. This approachutilizes the concept of a ‘Null’ which is simply the direction where thetransmitter perfectly corrects for its own Doppler shift. The same‘Nulling’ protocol runs on each node and scans through all directions,such as via a scanning sequence of a protocol. Here we arbitrarilyillustrate the scanning with discrete successive steps of 10 degrees butin a real system; however, it should be understood that any suitablestep size of degrees may be used for Doppler null scanning.

As already mentioned, one of the contributions of some embodiments ispassive spatial awareness. Traditionally, spatial information forneighbor nodes (based on a global positioning system (GPS) and/or gyrosand accelerometers) can be learned via data communication.Unfortunately, spatial awareness via data communication, referred to asactive spatial awareness is possible only after communication hasalready been established, not while discovering those neighbor nodes.Data communication is only possible after the signals for neighbor nodeshave been discovered, synchronized and Doppler corrected. In contrast,in some embodiments, the passive spatial awareness described herein maybe performed using only synchronization bits associated withacquisition. This process can be viewed as physical layer overhead andtypically requires much lower bandwidth compared to explicit datatransfers. The physical layer overheads for discovery, synchronizationand Doppler correction have never been utilized for topology learningfor upper layers previously.

Traditionally, network topology is harvested via a series of data packetexchanges (e.g., hello messaging and link status advertisements). Thepassive spatial awareness may eliminate hello messaging completely andprovide a wider local topology which is beyond the coverage of hellomessaging. By utilizing passive spatial awareness, highly efficientmobile ad hoc networking (MANET) is possible. Embodiments may improvethe functioning of a network, itself.

Referring to FIG. 1 , a multi-node communications network 100 isdisclosed. The multi-node communications network 100 may includemultiple communications nodes, e.g., a transmitter (Tx) node 102 and areceiver (Rx) node 104.

In embodiments, the multi-node communications network 100 may includeany multi-node communications network known in the art. For example, themulti-node communications network 100 may include a mobile ad-hocnetwork (MANET) in which the Tx and Rx nodes 102, 104 (as well as everyother communications node within the multi-node communications network)is able to move freely and independently. Similarly, the Tx and Rx nodes102, 104 may include any communications node known in the art which maybe communicatively coupled. In this regard, the Tx and Rx nodes 102, 104may include any communications node known in the art fortransmitting/transceiving data packets. For example, the Tx and Rx nodes102, 104 may include, but are not limited to, radios (such as on avehicle or on a person), mobile phones, smart phones, tablets, smartwatches, laptops, and the like. In embodiments, the Rx node 104 of themulti-node communications network 100 may each include, but are notlimited to, a respective controller 106 (e.g., control processor),memory 108, communication interface 110, and antenna elements 112. (Inembodiments, all attributes, capabilities, etc. of the Rx node 104described below may similarly apply to the Tx node 102, and to any othercommunication node of the multi-node communication network 100.)

In embodiments, the controller 106 provides processing functionality forat least the Rx node 104 and can include any number of processors,micro-controllers, circuitry, field programmable gate array (FPGA) orother processing systems, and resident or external memory for storingdata, executable code, and other information accessed or generated bythe Rx node 104. The controller 106 can execute one or more softwareprograms embodied in a non-transitory computer readable medium (e.g.,memory 108) that implement techniques described herein. The controller106 is not limited by the materials from which it is formed or theprocessing mechanisms employed therein and, as such, can be implementedvia semiconductor(s) and/or transistors (e.g., using electronicintegrated circuit (IC) components), and so forth.

In embodiments, the memory 108 can be an example of tangible,computer-readable storage medium that provides storage functionality tostore various data and/or program code associated with operation of theRx node 104 and/or controller 106, such as software programs and/or codesegments, or other data to instruct the controller 106, and possiblyother components of the Rx node 104, to perform the functionalitydescribed herein. Thus, the memory 108 can store data, such as a programof instructions for operating the Rx node 104, including its components(e.g., controller 106, communication interface 110, antenna elements112, etc.), and so forth. It should be noted that while a single memory108 is described, a wide variety of types and combinations of memory(e.g., tangible, non-transitory memory) can be employed. The memory 108can be integral with the controller 106, can comprise stand-alonememory, or can be a combination of both. Some examples of the memory 108can include removable and non-removable memory components, such asrandom-access memory (RAM), read-only memory (ROM), flash memory (e.g.,a secure digital (SD) memory card, a mini-SD memory card, and/or amicro-SD memory card), solid-state drive (SSD) memory, magnetic memory,optical memory, universal serial bus (USB) memory devices, hard diskmemory, external memory, and so forth.

In embodiments, the communication interface 110 can be operativelyconfigured to communicate with components of the Rx node 104. Forexample, the communication interface 110 can be configured to retrievedata from the controller 106 or other devices (e.g., the Tx node 102and/or other nodes), transmit data for storage in the memory 108,retrieve data from storage in the memory, and so forth. Thecommunication interface 110 can also be communicatively coupled with thecontroller 106 to facilitate data transfer between components of the Rxnode 104 and the controller 106. It should be noted that while thecommunication interface 110 is described as a component of the Rx node104, one or more components of the communication interface 110 can beimplemented as external components communicatively coupled to the Rxnode 104 via a wired and/or wireless connection. The Rx node 104 canalso include and/or connect to one or more input/output (I/O) devices.In embodiments, the communication interface 110 includes or is coupledto a transmitter, receiver, transceiver, physical connection interface,or any combination thereof.

It is contemplated herein that the communication interface 110 of the Rxnode 104 may be configured to communicatively couple to additionalcommunication interfaces 110 of additional communications nodes (e.g.,the Tx node 102) of the multi-node communications network 100 using anywireless communication techniques known in the art including, but notlimited to, GSM, GPRS, CDMA, EV-DO, EDGE, WiMAX, 3G, 4G, 4G LTE, 5G,WiFi protocols, RF, LoRa, and the like.

In embodiments, the antenna elements 112 may include directional oromnidirectional antenna elements capable of being steered or otherwisedirected (e.g., via the communications interface 110) for spatialscanning in a full 360-degree arc (114) relative to the Rx node 104 (oreven less than a full 360 degree arc).

In embodiments, the Tx node 102 and Rx node 104 may one or both bemoving in an arbitrary direction at an arbitrary speed, and maysimilarly be moving relative to each other. For example, the Tx node 102may be moving relative to the Rx node 104 according to a velocity vector116, at a relative velocity V_(Tx) and a relative angular direction (anangle α relative to an arbitrary direction 118 (e.g., due east); θ maybe the angular direction of the Rx node relative to due east.

In embodiments, the Tx node 102 may implement a Doppler nullingprotocol. For example, the Tx node 102 may adjust its transmit frequencyto counter the Doppler frequency offset such that there is no netfrequency offset (e.g., “Doppler null”) in a Doppler nulling direction120 (e.g., at an angle ϕ relative to the arbitrary direction 118). Thetransmitting waveform (e.g., the communications interface 110 of the Txnode 102) may be informed by the platform (e.g., the controller 106) ofits velocity vector and orientation (e.g., a, V_(T)) and may adjust itstransmitting frequency to remove the Doppler frequency shift at eachDoppler nulling direction 120 and angle ϕ.

To illustrate aspects of some embodiments, we show the 2D dependence ofthe net frequency shift for a stationary receiver as a function of Nulldirection across the horizon, as shown in a top-down view of FIG. 1 ,where the receiver node 104 is stationary and positioned 8 from eastrelative to the transmitter, the transmitter node 102 is moving with aspeed |

| and direction a from east and a snapshot of the scanning ϕ which isthe ‘Null’ direction, exemplarily shown as 100 degrees in this picture.

The Doppler shift is a physical phenomenon due to motion and can beconsidered as a channel effect. In this example the transmitter node 102is the only moving object, so it is the only source of Doppler shift.The Doppler frequency shift as seen by the receiver node 104 due to thetransmitter node 102 motion is:

${\frac{\Delta f_{DOPPLER}}{f} = {\frac{❘\overset{\rightarrow}{V_{T}}❘}{c}{\cos\left( {\theta - \alpha} \right)}}},$

where c is the speed of light

The other factor is the transmitter frequency adjustment term thatshould exactly compensate the Doppler shift when the ‘Null’ directionaligns with the receiver direction. It is the job of the transmitternode 102 to adjust its transmit frequency according to its own speed(|{right arrow over (V_(T))}|), and velocity direction (α). Thattransmitter frequency adjustment (Δf_(T)) is proportional to thevelocity projection onto the ‘Null’ direction (

) and is:

$\frac{\Delta f_{T}}{f} = {{- \frac{❘\overset{\rightarrow}{V_{T}}❘}{c}}{\cos\left( {\varphi - \alpha} \right)}}$

The net frequency shift seen by the receiver is the sum of the twoterms:

$\frac{\Delta f_{net}}{f} = {\frac{❘\overset{\rightarrow}{V_{T}}❘}{c}\left\lbrack {{\cos\left( {\theta - \alpha} \right)} - {\cos\left( {\varphi - \alpha} \right)}} \right\rbrack}$

It is assumed that the velocity vector and the direction changes slowlycompared to the periodic measurement of Δf_(net). Under thoseconditions, the unknown parameters (from the perspective of the receivernode 104) of α, |{right arrow over (V_(T))}|, and θ are constants.

Furthermore, it is assumed that the receiver node 104 has animplementation that resolves the frequency of the incoming signal, aswould be understood to one of ordinary skill in the art.

FIG. 2A shows the resulting net frequency shift as a function of the‘Null’ direction for scenarios where a stationary receiver is East ofthe transmitter (theta=0), and with a transmitter speed of 1500 metersper second (m/s). FIG. 2B shows the results for a stationary receiverand for several directions with an Eastern transmitter node velocitydirection (alpha=0). The frequency shifts are in units of parts permillion (ppm). As shown in FIGS. 2A and 2B, the amplitude is consistentwith the transmitter node's 102 speed of 5 ppm [|{right arrow over(V_(T))}|/c*(1×10⁶)] regardless of the velocity direction or position,the net frequency shift is zero when the ‘Null’ angle is in the receiverdirection (when ϕ=8), and the minimum occurs when the ‘Null’ is alignedwith the transmitter node's 102 velocity direction (when 1=a).

From the profile, the receiver node 104 can therefore determine thetransmitter node's 102 speed, the transmitter node's 102 heading, andthe direction of the transmitter node 102 is known to at most, one oftwo locations (since some profiles have two zero crossings). It shouldbe noted that the two curves cross the y axis twice (0 & 180 degrees inFIG. 2A, and ±90 degrees in FIG. 2B) so there is initially an instanceof ambiguity in position direction. In this case the receiver node 104knows the transmitter node 102 is either East or West of the receivernode 104.

Referring to FIG. 3 , a multi-node communications network 100 isdisclosed. The multi-node communications network 100 may includemultiple communications nodes, e.g., a transmitter (Tx) node 102 and areceiver (Rx) node 104. As shown in FIG. 3 both of the transmitter node102 and the receiver node 104 are in motion in two dimensions.

The simultaneous movement scenario is depicted in FIG. 3 where thereceiver node 104 is also moving in a generic velocity characterized bya speed |{right arrow over (V_(R))}| and the direction, β. The protocolfor the moving receiver node 104 incorporates a frequency adjustment onthe receiver node's 104 side to compensate for the receiver node's 104motion as well. The equations have two additional terms. One is aDoppler term for the motion of the receiver and the second is frequencycompensation by the receiver.

Again, the Doppler shift is a physical phenomenon due to motion and canbe considered as a channel effect, but in this case both the transmitternode 102 and the receiver node 104 are moving so there are two Dopplershift terms. The true Doppler shift as seen by the receiver due to therelative radial velocity is:

$\frac{\Delta f_{DOPPLER}}{f} = {{\frac{❘\overset{\rightarrow}{V_{T}}❘}{c}{\cos\left( {\theta - \alpha} \right)}} - {\frac{❘\overset{\rightarrow}{V_{R}}❘}{c}{\cos\left( {\theta - \beta} \right)}}}$

The other factors are the transmitter node 102 and receiver node 104frequency adjustment terms that exactly compensates the Doppler shiftwhen the ‘Null’ direction aligns with the receiver direction. It is thejob of the transmitter node 102 to adjust the transmitter node's 102transmit frequency according to its own speed (|{right arrow over(V_(T))}|), and velocity direction (α). That transmitter node frequencyadjustment is proportional to the velocity projection onto the ‘Null’direction (ϕ) and is the first term in the equation below.

It is the job of the receiver node 104 to adjust the receiver nodefrequency according to the receiver node's 104 own speed (|{right arrowover (V_(R))}|), and velocity direction (β). That receiver nodefrequency adjustment is proportional to the velocity projection onto the‘Null’ direction (

) and is the second term in the equation below. The receiver nodefrequency adjustment can be done to the receive signal prior to thefrequency resolving algorithm or could be done within the algorithm.

$\frac{\Delta f_{{T\&}R}}{f} = {{{- \frac{❘\overset{\rightarrow}{V_{T}}❘}{c}}{\cos\left( {\varphi - \alpha} \right)}} + {\frac{❘\overset{\rightarrow}{V_{R}}❘}{c}{\cos\left( {\varphi - \beta} \right)}}}$

The net frequency shift seen by the receiver is the sum of all terms:

$\frac{\Delta f_{net}}{f} = {{\frac{❘\overset{\rightarrow}{V_{T}}❘}{c}\left\lbrack {{\cos\left( {\theta - \alpha} \right)} - {\cos\left( {\varphi - \alpha} \right)}} \right\rbrack} - {\frac{❘\overset{\rightarrow}{V_{R}}❘}{c}\left\lbrack {{\cos\left( {\theta - \beta} \right)} - {\cos\left( {\varphi - \beta} \right)}} \right\rbrack}}$

Again, it is assumed that the receiver node 104 has an implementationthat resolves the frequency of the incoming signal, as would beunderstood in the art.

Also, it is assumed that the velocity vector and direction changesslowly compared to the periodic measurement of Δf_(net). Again, undersuch conditions, the unknown parameters (from the perspective of thereceiver node 104) α, |V_(T)|, and 0 are constants. When the velocityvector or direction change faster, then this change could be tracked,for example if the change is due to slow changes in acceleration.

The net frequency shift for the two-dimensional (2D) moving receivernode 104 approach is shown in FIGS. 4A and 4B for several scenario casesof receiver node location, θ, and transmitter node and receiver nodespeeds (|{right arrow over (V_(T))}| & |{right arrow over (V_(R))}|), aswell as transmitter node and receiver node velocity direction (α and β).FIG. 4A has different speeds for the transmitter node 102 and receivernode 104 as well as the receiver node location of θ=0. FIG. 4B has thesame speed for the transmitter node and receiver node. Similarly, thereare three concepts to notice here:

-   -   The amplitude is consistent with the relative velocity between        transmitter node 102 and receiver node 104 [|(|{right arrow over        (V_(T))}| cos (α)−|{right arrow over (V_(R))}| cos        (β))|/c*(1e6)].    -   The net frequency shift is zero when the ‘Null’ angle is in the        receiver direction (when ϕ=θ).    -   The minimum occurs when the ‘Null’ is aligned with the relative        velocity direction (when ϕ=angle(|{right arrow over (V_(T))}|        cos (α)−|{right arrow over (V_(R))}| cos (β)).

Again, there is an initial dual point ambiguity with the position, θ,but the transmitter node's 102 speed and velocity vector is known.

Referring now to FIG. 5 , while the 2D picture is easier to visualize,the same principles apply to the 3D case. FIG. 5 shows a number ofdirection sets needed to span 3D and 2D space with different cone sizes(cone sizes are full width). Before diving into the equations, it'sworth commenting on the size of the space when including anotherdimension. For example, when a ‘Null’ step size of 10 degrees was usedin the previous examples, it took 36 sets to span the 360 degrees in 2D.Thus, if an exemplary detection angle of 10 degrees is used (e.g., adirectional antenna with 10-degree cone) it would take 36 sets to coverthe 2D space. The 3D fractional coverage can be computed by calculatingthe coverage of a cone compared to the full 4 pi steradians. Thefraction is equal to the integral

${{FractionCoverage}3D} = {\frac{\int_{0}^{{ConeSize}/2}{r^{2}\sin\left( \theta^{\prime} \right)d\theta^{\prime}d_{\varphi}}}{4\pi r^{2}} = \frac{1 - {\cos\left( {{ConeSize}/2} \right)}}{2}}$FractionCoverage2D = 2π/ConeSize

The number of sets to span the space is shown in FIG. 5 for both the 2Dand 3D cases which correlates with discovery time. Except for narrowcone sizes, the number of sets is not drastically greater for the 3Dcase (e.g., approximately 15 times at 10 degrees, 7 time at 20 degrees,and around 5 times at 30 degrees). Unless systems are limited to verynarrow cone sizes, the discovery time for 3D searches is notoverwhelming compared to a 2D search.

Referring now to FIG. 6 , a multi-node communications network 100 isdisclosed. The multi-node communications network 100 may includemultiple communications nodes, e.g., a transmitter (Tx) node 102 and areceiver (Rx) node 104. As shown in FIG. 6 both of the transmitter node102 and the receiver node 104 are in motion in three dimensions.

The 3D approach to Doppler nulling follows the 2D approach but it isillustrated here with angles and computed vectorially for simplicity.

In three dimensions, it is convenient to express the equations in vectorform which is valid for 2 or 3 dimensions. FIG. 6 shows the geometry in3 dimensions where

is the unit vector pointing to the receiver from the transmitter, and

is the unit vector pointing in the ‘Null’ direction defined by theprotocol.

The true Doppler shift as seen by the receiver node 104 due to therelative radial velocity which is the projection onto the

vector:

$\frac{\Delta f_{DOPPLER}}{f} = {{\frac{1}{c}{\overset{\rightarrow}{V_{T}} \cdot}} - {\frac{1}{c}{\overset{\rightarrow}{V_{R}} \cdot}}}$

The nulling protocol adjusts the transmit node frequency and receivernode frequency due to their velocity projections onto the

direction

$\frac{\Delta f_{T}}{f} = {{{- \frac{1}{c}}{\overset{\rightarrow}{V_{T}} \cdot}} + {\frac{1}{c}{\overset{\rightarrow}{V_{R}} \cdot}}}$

The net frequency shift seen by the receiver node 104 is the sum of allterms:

$\frac{\Delta f_{net}}{f} = {{\frac{1}{c}{\overset{\rightarrow}{V_{T}} \cdot}} - {\frac{1}{c}{\overset{\rightarrow}{V_{R}} \cdot}} - {\frac{1}{c}{\overset{\rightarrow}{V_{T}} \cdot}} + {\frac{1}{c}{\overset{\rightarrow}{V_{R}} \cdot}}}$

The net frequency shift for the 3D moving receiver node 104 approach isnot easy to show pictorially but can be inspected with mathematicalequations to arrive at useful conclusions. The first two terms are theDoppler correction (DC) offset and the last two terms are the nulldependent terms. Since the

is the independent variable, the maximum occurs when ({right arrow over(V_(R))}−{right arrow over (V_(T))}) and

are parallel and is a minimum when they are antiparallel. Furthermore,the relative speed is determined by the amplitude,

${Amplitude} = {\frac{1}{c}{❘{\overset{\rightarrow}{V_{R}} - \overset{\rightarrow}{V_{T}}}❘}}$

Lastly, the net frequency is zero when the

is parallel (i.e., parallel in same direction, as opposed toanti-parallel) to

.

${\frac{\Delta f_{net}}{f} = {0{when}}},$${{{\frac{1}{c}{\overset{\rightarrow}{V_{T}} \cdot}} - {\frac{1}{c}{\overset{\rightarrow}{V_{R}} \cdot}}} = {{\frac{1}{c}{\overset{\rightarrow}{V_{T}} \cdot}} - {\frac{1}{c}{\overset{\rightarrow}{V_{R}} \cdot}{or}}}},$$\left. {{\left. {\overset{\rightarrow}{\left( V_{T} \right.} - \overset{\rightarrow}{V_{R}}} \right) \cdot} = {\overset{\rightarrow}{\left( V_{T} \right.} - \overset{\rightarrow}{V_{R}}}} \right) \cdot$

For the 3D case:

-   -   The amplitude is consistent with the relative velocity between        transmitter node 102 and receiver node 104 [|V_(R) −{right arrow        over (V_(T))}|/c].    -   The net frequency shift is zero when the ‘Null’ angle is in the        receiver node direction, ({right arrow over (V_(T))}−{right        arrow over (V_(R))})·        =({right arrow over (V_(T))}−{right arrow over (V_(R))})·        ).    -   The minimum occurs when the ‘Null’ is aligned with the relative        velocity direction.

Referring still to FIG. 6 , in some embodiments, the system (e.g., themulti-node communications network 100) may include a transmitter node102 and a receiver node 104. Each node of the transmitter node 102 andthe receiver node 104 may include a communications interface 110including at least one antenna element 112 and a controller operativelycoupled to the communications interface, the controller 106 includingone or more processors, wherein the controller 106 has information ofown node velocity and own node orientation. The transmitter node 102 andthe receiver node 104 may be in motion (e.g., in two dimensions or inthree dimensions). The transmitter node 102 and the receiver node 104may be time synchronized to apply Doppler corrections associated withsaid node's own motions relative to a common reference frame (e.g., acommon inertial reference frame (e.g., a common inertial reference framein motion or a stationary common inertial reference frame)). The commonreference frame may be known to the transmitter node 102 and thereceiver node 104 prior to the transmitter node 102 transmitting signalsto the receiver node 104 and prior to the receiver node 104 receivingthe signals from the transmitter node 102. In some embodiments, thesystem is a mobile ad-hoc network (MANET) comprising the transmitternode 102 and the receiver node 104.

In some embodiments, the applying of the Doppler corrections associatedwith the receiver node's own motions relative to the common referenceframe is based on a common reference frequency. For example, a commonreference frequency may be adjusted by a node's own motions to cancelout those motions in reference to the null angle. This common referencefrequency may be known by each node prior to transmission and/orreception of the signals. In some embodiments, calculating the netfrequency change seen by the receiver node 104 is based on the commonreference frequency. For example, the net frequency change may be adifference between a measured frequency of the signals and the commonreference frequency.

For purposes of discussing the receiver node 104, a “source” generallyrefers to a source of a received signal, multiple sources of multiplesignals, a single source of multiple signals, and/or the like. Forexample, a source may be a transmitter node 102 configured to applyDoppler corrections as disclosed herein and in applications from whichpriority is claimed and/or incorporated by reference. In this regard, areceiver node 104 may determine one or more attributes of the source(e.g., bearing between the receiver node 104 and the source, bearing ofthe velocity of the source, amplitude/speed of the velocity, range, andthe like). In some embodiments, the receiver node 104 and the source(e.g., transmitter node 102) are configured to use a same, compatible,and/or similar Doppler correction, protocol, common reference frame,common reference frequency, time synchronization, and/or the like suchthat the receiver node 104 may determine various attributes of thesource. Note, in some embodiments, that one or more of these may beknown ahead of time, be determined thereafter, included as fixedvariable values as part of the protocol, and/or determined dynamically(in real time) as part of the protocol. For example, the protocol maydetermine that certain common reference frames should be used in certainenvironments, such as using GPS coordinates on land and a naval shipbeacon transmitter common reference frame location (which may be mobile)over certain areas of ocean, which may dynamically change in real timeas a location of a node changes.

In some embodiments, the transmitter node 102 and the receiver node 104are time synchronized via synchronization bits associated withacquisition. For example, the synchronization bits may operate asphysical layer overhead.

In some embodiments, the transmitter node 102 is configured to adjust atransmit frequency according to an own speed and an own velocitydirection of the transmitter node 102 so as to perform atransmitter-side Doppler correction. In some embodiments, the receivernode 104 is configured to adjust a receiver frequency of the receivernode 104 according to an own speed and an own velocity direction of thereceiver node 104 so as to perform a receiver-side Doppler correction.In some embodiments, an amount of adjustment of the adjusted transmitfrequency is proportional to a transmitter node 102 velocity projectiononto a Doppler null direction, wherein an amount of adjustment of theadjusted receiver frequency is proportional to a receiver node 104velocity projection onto the Doppler null direction. In someembodiments, the receiver node 102 is configured to determine a relativespeed between the transmitter node 102 and the receiver node 104. Insome embodiments, the receiver node 104 is configured to determine adirection that the transmitter node 102 is in motion and a velocityvector of the transmitter node 102. In some embodiments, a maximum netfrequency shift for a Doppler correction by the receiver node 104 occurswhen a resultant vector is parallel to the Doppler null direction,wherein the resultant vector is equal to a velocity vector of thereceiver node 104 minus the velocity vector of the transmitter node 102.In some embodiments, a minimum net frequency shift for a Dopplercorrection by the receiver node 104 occurs when a resultant vector isantiparallel to the Doppler null direction, wherein the resultant vectoris equal to a velocity vector of the receiver node 104 minus thevelocity vector of the transmitter node 102. In some embodiments, a netfrequency shift for a Doppler correction by the receiver node 104 iszero when a vector pointing to the receiver node from the transmitternode 102 is parallel to the Doppler null direction.

Referring now to FIG. 7 , an exemplary embodiment of a method 700according to the inventive concepts disclosed herein may include one ormore of the following steps. Additionally, for example, some embodimentsmay include performing one or more instances of the method 700iteratively, concurrently, and/or sequentially. Additionally, forexample, at least some of the steps of the method 700 may be performedin parallel and/or concurrently. Additionally, in some embodiments, atleast some of the steps of the method 700 may be performednon-sequentially.

A step 702 may include providing a transmitter node and a receiver node,wherein each node of the transmitter node and the receiver node are timesynchronized, wherein each node of the transmitter node and the receivernode are in motion, wherein each node of the transmitter node and thereceiver node comprises a communications interface including at leastone antenna element, wherein each node of the transmitter node and thereceiver node further comprises a controller operatively coupled to thecommunications interface, the controller including one or moreprocessors, wherein the controller has information of own node velocityand own node orientation.

A step 704 may include based at least on the time synchronization,applying, by the transmitter node, Doppler corrections to thetransmitter node's own motions relative to a common reference frame.

A step 706 may include based at least on the time synchronization,applying, by the receiver node, Doppler corrections to the receivernode's own motions relative to the common reference frame, wherein thecommon reference frame is known to the transmitter node and the receivernode prior to the transmitter node transmitting signals to the receivernode and prior to the receiver node receiving the signals from thetransmitter node.

Further, the method 700 may include any of the operations disclosedthroughout.

The null scanning technique discussed herein illustrates a system and amethod for spatial awareness from resolving the temporal spatialcharacteristics of the transmitter node's 102 radiation. This approachinforms the receiver node 104 of the relative speed between thetransmitter node 102 and receiver node 104 as well as the transmitternode direction and transmitter node velocity vector. This approachincludes scanning through all directions and has a high sensitivity(e.g., low net frequency shift) when the null direction is aligned withthe transmitter node direction. This approach can be implemented on ahighly sensitive acquisition frame which is typically much moresensitive than explicit data transfers which allow for theultra-sensitive spatial awareness with relatively low power.

This sentence may mark an end to the (at least partially) reproducedlanguage from U.S. patent application Ser. No. 17/857,920 correspondingto the (at least partially) reproduced FIGS. 1-7 . However, note thatthis paragraph is nonlimiting, and changes may have been made andlanguage added or removed, and not all the language above orcorresponding figures are necessarily reproduced from U.S. patentapplication Ser. No. 17/857,920.

Directional radio frequency (RF) networks often must spend significanttime scanning the physical space over which potential RF network signalsmay exist. For example, a system scanning spherical space in azimuth andelevation may require numerous discrete time intervals to accomplish thetask. Generally, a receiver dwells for a finite amount of time withineach spatial sector looking for a desired signal; hence, total discoverytime becomes dwell time multiplied by the number of discrete timeintervals needed for the receiver to search the entire physical space.Because scanning may be a lengthy process, often it becomes necessary tosacrifice other important system performance metrics to ensure timelydiscovery performance.

Directional doppler nulling may be an enabling technology for reducingdiscovery time within directional networks, thereby allowing forimprovement in other performance metrics as well. Because of thesignificantly improved discovery time, directional Doppler-nulling mayalso be enabling technology for low-probability of detection (LPD)directional networks.

Transmission of explicit position information (e.g., GPS coordinatesusing two-way higher-bandwidth communications) and/or velocityinformation is not necessarily needed to obtain such information whenusing Doppler-nulling. In embodiments, Doppler is minimized (or“nulled”) via Doppler corrections in each direction an antenna ispointing based on at least a velocity of a node (e.g., which may beequally true for transmitter and receiver). Further, improvedcommunication between nodes becomes possible whenever antennas arepointing toward each other. In embodiments, range to another node can bedetermined from the use of precisely-defined transmission intervals, asthe transmission time in each can be known, a priori, to both thetransmitter and receiver. With bearing angle, range, and relativevelocity between nodes known via the Doppler-nulling protocol, itbecomes possible to precisely discover and track another node's positionwithout using any explicit data transfer (e.g., WiFi, Bluetooth, longerrange similar bandwidth aerospace communication protocols, and/or thelike).

The deep-noise addition to Doppler-nulling (e.g., U.S. patentapplication Ser. No. 17/534,061) may offer a viable mechanism forterminals to synchronize across long distances using very low power,thus minimizing potential for transmitter observation by anout-of-network receiver or interference to an out-of-network receiver.

In embodiments (i.e., in at least some embodiments) withDoppler-nulling, both the transmitting terminal (e.g., Tx node 102) andthe receiving terminal can initially use rather wide beams in order tofacilitate terminal discovery and establish an initialterminal-to-terminal link. In embodiments, it then becomes possible tonarrow the beam to allow high data rate communications with increasedtransmitter effective isotropic radiated power (EIRP) within the highergain smaller spot beam coverage. In this regard, an advantage of thepresent disclosure is that Doppler-nulling may support relativelyprecise antenna pointing for high gain narrow highly-focused antennabeams. Higher data rate communication over longer distance is thuspossible with the narrow spot beam pattern than could have been achievedwith a broader beam typically used for timely initial discovery andacquisition.

In embodiments, the Doppler-nulling technique allows each platform(e.g., node) to correct own-platform Doppler. In general, in at leastsome embodiments, exchanging position and velocity information betweenplatforms is unnecessary with directional Doppler-nulling; thus, lesssignal-in-space overhead is needed to maintain communication, fewersignal tracking resources are required, and there is reduced (or zero)inherent time lag in tracking. Relative position information may bediscerned from the periodic Doppler-nulling pulses which enable accurateantenna pointing between platforms.

Examples of doppler nulling methods include, but are not limited to,methods and other descriptions (e.g., at least some theory andmathematical basis) are disclosed in U.S. patent application Ser. No.17/233,107, filed Apr. 16, 2021, which is hereby incorporated byreference in its entirety; U.S. patent application Ser. No. 17/534,061,filed Nov. 23, 2021, which is hereby incorporated by reference in itsentirety; and U.S. patent application Ser. No. 17/857,920, filed Jul. 5,2022, which is hereby incorporated by reference in its entirety. Inembodiments, doppler nulling methods allow for benefits such as, but notlimited to, relatively quickly and/or efficiently detecting transmitternodes and determining transmitter node attributes (e.g., transmitternode speed, transmitter node bearing, relative bearing of transmitternode relative to receiver node, relative distance of transmitter noderelative to receiver node, and the like). Embodiments of the presentdisclosure may extend doppler nulling using directional systems toachieve relatively large efficiency improvements (e.g., lower powerrequirements, farther range, faster discovery times, and/or the like).

Because Doppler-nulling doesn't necessarily require an explicit digitaldata information transfer, directional Doppler-nulling may allow fordiscovery of network nodes scattered throughout a large physical spaceusing less energy than is possible with more conventional techniquesrelying on explicit digital data transfer.

Moreover, without node-to-node transfer of digital information,Doppler-nulling may offer an order-of-magnitude signal detectionimprovement compared to conventional systems utilizing digital data toexchange position and velocity information. In some embodiments, interms of distance, such performance improvements correspond with a rangeincrease of about three times (or more) in favor of the Doppler-nullingapproach.

The order-of-magnitude performance differential may correspond with anapproximately 10 dB advantage for Doppler-nulling which can be used toexpedite network routing significantly. Alternatively, when a threetimes range advantage is not needed, discovery power could be lowered by10 dB while still retaining the full system range needed for subsequentdigital data transfer. Lower power transmission during discovery meansless interference in directions where no network nodes exist and alsoless chance for the discovery signal to be detected by adversarialsystems.

In embodiments, to achieve a detection time improvement, a 10 dB poweradvantage might be distributed over 10 times the discovery space (i.e.,using a wider transmit beam); thus, allowing discovery to be conductedin only 10% the time needed for a conventional system. Upon discoveryand acquisition, the directional transmit beam could then quickly benarrowed to support higher speed data transfer at the same distance.

In embodiments, directional Doppler-nulling allows each node in adirectional network to compensate for its own individual Doppler shift,whether in the direction of transmission or the direction of reception.This is a simpler arrangement than requiring either the transmitter orthe receiver to correct all system Doppler.

In embodiments, directional systems with Doppler-nulling may operatewith some constraints, as the received signal may be unlikely to remainabove the noise level except when transmit antenna and receive antennapoint generally in the direction of each other. Thus, maximum signalstrength may only periodically be available at the intended receiver.Fortunately, antenna directionality can be combined withDoppler-nulling, via embodiments of the present disclosure, to enableincreased sensitivity at the moments during the Doppler-nulling scanwhen the transmit antenna and the receive antenna point generally towardeach other. At these moments during the scan, communication betweennodes becomes possible.

Referring to FIG. 10 , a graphical representation 1000 of an angulardistribution of antenna gain 1002 versus angle (e.g., receiving angle ofa signal) is illustrated, according to one or more embodiments of thepresent disclosure. For example, an alignment of antenna directivity ofa receiver node 104 and/or transmitter node 102 is illustrated. Asdescribed below for FIG. 11 , a peak antenna gain 1004 bearing angle(e.g., first bearing angle) may be used to determine bearing angle andcombined with Doppler nulling methods bearing angles (e.g., secondbearing angle) to achieve a more precise bearing angle.

FIG. 10 shows antenna gain 1002 for a single transmit or receive antennaelement across 360 degrees. Combining antenna gain for both a receivernode and transmitter node pointing at each other would result in doublethe decibels of antenna gain 1002. Therefore, in this way, aligning bothdirectional antennas provides a generally desirable high antenna gaincompared to omnidirectional (unaligned) antennas or only one alignedantenna. However, aligning the antenna using other conventional methodsoften requires time-consuming and inefficient scanning patterns and maynot result in a precise/narrow estimate of bearing angle.

FIG. 11 shows a graphical representation 1100 of net frequency shiftpoints 1104 and a frequency shift profile 1102 (e.g., function)including a zero crossing 1106 based on the net frequency shift points1104, according to one or more embodiments of the present disclosure.

Generally, in embodiments, in contrast to a rather less preciseamplitude peak 1004 generally achievable with directional antennapointing alone, Doppler-nulling may be used to generate a moresharply-defined and/or faster estimation of bearing angle as shown bythe zero crossing 1106 as seen in FIG. 11 . The peak 1004 of a smoothcurve of antenna gain 1002 is generally more difficult to pin-point thana zero crossing/intersection point of two lines. The zero crossing 1106crosses zero at about 110 degrees. In embodiments, the zero crossing1106 may be used alone, and/or in combination with the amplitude peak1004 from antenna pointing to provide a more precise indication ofbearing angle between nodes than is possible using antenna pointingalone.

In embodiments, Doppler-nulling may allow for determining the netfrequency shift points 1104. Consider a nonlimiting scenario of a staticreceiver node 104. In such a scenario, a net frequency shift point 1104may be a value indicative of a difference between a (known) commonreference frequency and a measured frequency of a received pulse. See,e.g., pulse 804 in FIG. 8 . Conceptually, this difference may be zero ifthe transmitter node 102 happens to direct the pulse perfectly at thereceiver node 104 and applies a Doppler correction associated with thetransmitter node's 102 own motions to cancel out real-world physicallyinduced Doppler effects on the pulse (i.e., equal to zero when thestatic receiver's measured pulse frequency=common reference frequency).Furthermore, if the common reference frame is also static over time andif the pulse is close to being aimed at the receiver 104 (e.g., within 6degrees), then the net frequency shift points 1104 may have a value thatis “near zero”. The labeled points 1104 in FIG. 11 are “near zero” netfrequency shift points 1104. Such points 1104 may, for example, be usedto generate a function such as a linear line which is fit to the points1104, or any other function (e.g., sinusoidal function). Next, such afunction may be used to solve for (e.g., interpolate) the zero crossing1106 using any interpolation method known in the art. In this regard,one or more net frequency shift points 1104, such as “zero-relatedvalues” comprising: “zero”, “zero crossing” 1106″, and/or “near zero”values/functions or the like may be used to determine a bearing angle(θ) between the receiver node 102 and a source (e.g., transmitter node102).

In embodiments, the function/slope 1102 may be generated using netfrequency shift points 1104. For instance, the function may be asinusoidal function, a linear function fitted to the net frequency shiftpoints 1104 using any fitting function known in the art, or the like.

By using a zero-crossing the function/slope 1102, a continuousinterpolation between coarse antenna pointing angle increments issupported, and thus a more precise indication of bearing angle may beachieved compared to signal amplitude alone at successive antennapositions. A (limited segment) of a zero-crossing 1106 may be determinedusing a few (e.g., 2 or more) points 1104 may allow forreconstruction/extrapolation/curve-fitting of an entire Doppler netfrequency profile 1102 using just the few sample points 1104. Inembodiments, both bearing and differential velocity may be derived fromthe approximated frequency shift profile 1102 using three or more datapoints 1104. (Note that such a three data point requirement may imply,in some embodiments, some overlap in coverage between subsequent antennabeams. At least three points are generally needed to approximate acurve, but a larger number of data points for a curve may be available.)

FIG. 8 is a time-based graphical representation 800 of a plurality ofpulses 804 of a scanning sequence 802, according to one or moreembodiments of the present disclosure. For example, any quantity ofpulses 804 in various directions (e.g., 2D, 3D) may be used. Note thatthe sequence may be incremental (e.g., 10 degrees, 20 degrees, 30degrees, etc.), pseudo-random (e.g., a random pattern known by allnodes, a priori, according to a protocol; 10 degrees, 240 degrees, 40degrees, etc.), and/or the like.

In embodiments, a quantity of the plurality of pulses 804 is generallybetween 2 and 300. (Note that similarly to the Nyquist criteria, theminimum number of required points for reconstructing the sine wave hereis greater than two. Rapid acquisition over a single cycle requires, forpractical purposes, three pulses. The upper end for number of samples,while technically unbounded, like any other over-sampled system exhibitsdiminishing returns after an order of magnitude or two. As a result, arealistic upper end for number of samples per cycle is around 300.) Forexample, the quantity may be 32 as shown. In another example, thequantity may vary according to fixed sequence patterns and/or accordingto any protocol variables (e.g., type of desired receiver node (e.g.,drone, aircraft, cellular device, etc.), type of transmitter node,location, time of day, and/or the like). For instance, different typesof devices may be configured to use different scanningsequences/protocols. By way of another example, a sequence may cyclebetween using a lower quantity of wide beams and then a higher qualityof narrow beams. Note that such examples are nonlimiting and anyscanning sequence (or subsets of scanning sequences) at any time may beused based on any method.

Generally, the phrase “the signals correspond to at least a portion ofthe pulses 804”, and the like, means that the signals (e.g., receivedwaveforms from antenna element, etc.) correspond to (e.g., could bepaired to, and/or are generated based on) at least a portion of a set oftheoretical pulses 804 of a scanning sequence 802 used to generate thesignals. For example, if both a source (e.g., transmitter node 102) andreceiver node 104 are synced to a scanning sequence 802, then thereceiver node 104 may be configured to parse the (received) signals intopulses 804 that could be mapped/paired to the pulses 804 of the scanningsequence 802. Here, a “portion” of the set of theoretical pulses 804means that not all of the pulses 804 are necessarily received.

“Time synced” and the like may mean that each node is aware of anabsolute time within a cycle of a scanning sequence 802 such that anytime-of-arrival of a received pulse 804 may be mapped to its location ina graphical representation 800 of the scanning sequence or the like(e.g., mapped along the horizontal axis of FIG. 11 ). For example, acontroller may keep track of an absolute sync time and a local receivetime, such that the local receive time may be converted to the absolutesync time. Such a corresponding relationship may be used, as shown inFIG. 8 and FIG. 11 , to determine a transmitting angle (e.g., ϕ1, ϕ2, ϕ3. . . ). Such time-of-arrival syncing isn't necessarily perfectlyaccurate or predictable. For example, the scanning sequence may includetransmitter node and receiver node time uncertainty (error) margins 806,810 on either side of the pulse 804 and/or a propagation time margin 812(e.g., to account for differences in range between nodes). By usingmargins of time, each received pulse 804 may more accurately be pairedto the correct corresponding pulse 804 illustrated in the scanningsequence 802 of FIG. 8 .

In some embodiments, example parameters may allow for a reliable spatialawareness up to a range of around 300 miles (e.g., 200 miles or more,290 miles or more). For example, such parameters may include: a quantityof thirty-two pulses 804 horizontally scanned a full 360 degrees, apulse width 808 of 100 microseconds (μsec), transmitter node andreceiver node time uncertainty (error) margins 806, 810 of 1,000 μsec.Other determined (e.g., derived) parameters may include: a propagationdelay of 1,610 μsec, a pulse repetition interval of 5,710 μsec., a pulseduty cycle of 1.75%, and a quantity of five scans (e.g., each scan beinga scan cycle around 360 degrees) per second corresponding to a duration814 of 0.20 seconds.

In some examples, the duration 814 may be less than one second, and/orgreater than one second.

FIG. 9A is a diagrammatic illustration 900 of multiple systems 100(e.g., 100 a, 100 b, 100 c, 100 d) according to one or more embodimentsof the present disclosure. Each system 100 is configured to transmit andreceive, such as via one or more directional antenna elements. In asense, each system 100 may comprise a transmitter node and a receivernode (e.g., 102 a,104 a; 102 b,104 b; 102 c,104 c; 102 d,104 d), whichcould be the same node. If the systems 100 are time synced, then eachsystem 100 is configured to receive a plurality of received pulses 804from every other system along a receiving angle associated with each ofthe other systems 100 according to a scanning sequence 802, therebyincreasing effective antenna gain. In theory, if each system 100 wastime synced and desired to have spatial awareness of other time syncedsystems, then the system 100 could more efficiently improve antenna gainof receivable pulses by only searching for signals according to thescanning sequence 802, vastly reducing the angles/space to search forsignals from. In this way, each system would only search for signals ina direction at the same time that nodes from that direction would bereciprocally transmitting—improving efficiency, range, and reducingnoise produced by less efficient scanning techniques.

FIG. 9B is a diagrammatic illustration 920 of FIG. 9A at a subsequenttime step where a particular transmitting angle 804 b and receivingangle 904 c of different systems 100 b, 100 c are aligned or nearlyaligned (e.g., within a detectable beam width).

In embodiments, each system 100 is time synchronized to utilize a commonscanning sequence 802 such that the receiving angles 904 a-904 d (e.g.,null Rx) and transmitting angles 804 a-804 d (e.g., null Tx angle ϕ) ofeach system will align at particular steps in the scanning sequence 802.For example, as shown, the receiving angles 904 a-904 d of all systems100 may be opposite relative to the transmitting angles 804 a-804 dduring some or the entire execution of the scanning sequence 802. Asdescribed previously in regard to FIG. 10 , this may allow twice theeffective antenna gain due to alignment.

It is to be understood that embodiments of the methods disclosed hereinmay include one or more of the steps described herein. Further, suchsteps may be carried out in any desired order and two or more of thesteps may be carried out simultaneously with one another. Two or more ofthe steps disclosed herein may be combined in a single step, and in someembodiments, one or more of the steps may be carried out as two or moresub-steps. Further, other steps or sub-steps may be carried in additionto, or as substitutes to one or more of the steps disclosed herein.

Although inventive concepts have been described with reference to theembodiments illustrated in the attached drawing figures, equivalents maybe employed and substitutions made herein without departing from thescope of the claims. Components illustrated and described herein aremerely examples of a system/device and components that may be used toimplement embodiments of the inventive concepts and may be replaced withother devices and components without departing from the scope of theclaims. Furthermore, any dimensions, degrees, and/or numerical rangesprovided herein are to be understood as non-limiting examples unlessotherwise specified in the claims.

We claim:
 1. A system comprising: a receiver node comprising: acommunications interface comprising a directional antenna element; and acontroller operatively coupled to the communications interface, thecontroller including one or more processors, wherein the controller hasinformation of own node velocity and own node orientation relative to acommon reference frame; wherein the receiver node is time synchronizedto apply Doppler corrections associated with the receiver node's ownmotions relative to the common reference frame, wherein the commonreference frame is known to the receiver node prior to the receiver nodereceiving signals from a source.
 2. The system of claim 1, wherein thesystem is configured to determine one or more net frequency shift pointsbased on the signals.
 3. The system of claim 2, wherein the determiningof the one or more net frequency shift points is based on a scanningsequence known to the receiver node, wherein the signals correspond toat least a portion of a plurality of pulses of the scanning sequence. 4.The system of claim 3, wherein the receiver node is configured todetermine a transmitting angle of a particular pulse based on atime-of-arrival of the particular pulse within the scanning sequence. 5.The system of claim 3, wherein a quantity of the plurality of pulses ofthe scanning sequence is at least
 2. 6. The system of claim 3, whereinthe plurality of pulses is configured to span a full 360 degrees in atleast one of azimuth, or elevation.
 7. The system of claim 3, wherein aduration of one cycle of the scanning sequence is less than a second. 8.The system of claim 2, wherein the system is configured to determine abearing angle between the receiver node and the source, wherein thebearing angle is based on a zero-related value associated with the oneor more net frequency shift points, wherein the zero-related valuecomprises at least one of: a zero crossing of a function based on theone or more net frequency shift points; or a zero value and/or near zerovalue of the one or more net frequency shift points.
 9. The system ofclaim 8, wherein the system is configured to narrow a beam width of anew signal transmitted by the system in the direction of the bearingangle between the receiver node and the source, and establish a two-waycommunication link with the source.
 10. The system of claim 2, whereinthe system is configured to determine a bearing angle between thereceiver node and the source, wherein the bearing angle is based on afirst bearing angle and a second bearing angle, wherein the firstbearing angle is based on an angular distribution of antenna gain of thesignals, and wherein the second bearing angle is based on the one ormore net frequency shift points determined based on the signals.
 11. Thesystem of claim 2, wherein the one or more net frequency shift pointsare based on a difference between a common reference frequency known tothe system and one or more measured frequencies of the signals.
 12. Asystem comprising: a transmitter node comprising: a communicationsinterface comprising a directional antenna element; and a controlleroperatively coupled to the communications interface, the controllerincluding one or more processors, wherein the controller has informationof own node velocity and own node orientation relative to a commonreference frame; wherein the transmitter node is time synchronized toapply Doppler corrections associated with the transmitter node's ownmotions relative to the common reference frame, wherein the commonreference frame is known to the transmitter node prior to thetransmitter node transmitting signals.
 13. The system of claim 12,wherein the applying of the Doppler corrections comprises applying theDoppler corrections based on a common reference frequency.
 14. Thesystem of claim 12, wherein the system is configured to transmit aplurality of transmitted pulses of the signals along a plurality oftransmitting angles according to a scanning sequence, wherein theapplying of the Doppler corrections comprises applying the Dopplercorrections to the plurality of transmitted pulses based on atransmitting angle of each transmitted pulse.
 15. The system of claim14, wherein a quantity of the plurality of pulses is at least
 2. 16. Thesystem of claim 14, wherein the plurality of pulses is configured tospan 360 degrees in at least one of azimuth or elevation.
 17. The systemof claim 14, wherein a duration of the scanning sequence is less than asecond.
 18. The system of claim 14, wherein, for received signals, thesystem is time synchronized to apply the Doppler corrections associatedwith the transmitter node's own motions relative to the common referenceframe to the received signals via an antenna element configured toreceive the received signals.
 19. The system of claim 18, wherein thesystem is configured to receive a plurality of received pulses of thereceived signals along a plurality of receiving angles according to thescanning sequence.
 20. The system of claim 19, wherein the receivingangles are opposite relative to the transmitting angles during anexecution of the scanning sequence.